Patrick,
The proximity of the fw bunker to the green would pose the biggest safety issue. If you pushed two fw closer together just to make one bunker, they might be too close.
The church pews were extended at both ends by Fazio before the recent US Open to keep them relevant.
The biggest problem with combining bunkers, IMHO, is that they need to tip different directions on opposing holes to be visible and provide a lip to hinder escape. The pews get over this by being extended great lengths. Ross has a big U shaped bunker at Inverness serving two holes, but its not smaller than two bunkers would be, its just connected at the end. So, its actually a little larger than non connected bunkers would be.
FWIW, I once lost a design commission based on a preliminary rendering I did that showed a cluster of bunkers between two parallel and same direction fw, much like Inverness 1 and 10. The committee commented on the safety issues, despite me saying the fw were as far apart as typical fw and the interview went downhill from there.........